Construction sites frequently include excavations in the form of ditches and holes to be used in the construction process. Such ditches and holes present a safety hazard whenever they must be left open, particularly at a time when construction crews are not present. Safety regulations currently in place in most locations in the United States require some type of warning or cover to be placed on such ditches or holes to prevent potential injury. In addition, covers are used to prevent vandalism or accidental damage to the ditch or hole.
Current methods which are used to provide safety or warning of the presence of a hole range from a taping off or fencing off of the region in which the hole is located, or covering the hole with plywood, pallets or the like. If warning tapes or plywood sheets are used, dangers still exist if children or vandals uncover the hole, creating the potential for injuries and consequent liabilities.
Manhole covers for permanent manhole installations exist. Typically, manhole covers are made in the form of a very heavy, circular plate, which closely fits into a recess around the lip of the manhole. Such plates require special tools or relatively heavy machinery in order to remove them. A locking manhole insert or a locking manhole cover for suspending equipment beneath a cover is disclosed in the Wisniewski U.S. Pat. No. 5,328,291. This patent discloses a safety cover for manholes which is to be placed beneath a conventional manhole cover. The safety cover disclosed in the Wisniewski patent includes a plurality of arms which may be extended outwardly by rotating a central cam. A provision then is made in this patent for locking the arms in place with a padlock; so that the cover cannot be removed, since the arms extend under the lip of the manhole opening. The cover has chains attached to its underside for holding a container of equipment in suspension beneath the cover.
The Kagstrom U.S. Pat. No. 4,101,154 discloses a hole cover for well holes or the like. The hole cover is equipped with a self-locking mechanism in it. The locking mechanism comprises at least a pair of diametrically opposed arms, which are pivotally attached to a central shaft extending downwardly from the center of the well cover. These arms have a length chosen to cause them to slidably engage the wall of the hole when the cover is placed over the hole. The arms are not driven into the side walls of the hole; but if an attempt is made to remove the cover, the arms tend to pivot more tightly to engage the sides of the hole, preventing removal of the cover. When removal is desired, a rod or key is inserted through an aperture in a central tube attached to the cover to engage the lower ends of the pivoting arms to readily move them out of engagement with the hole. When the rod is in place, the cover then readily can be removed. The arms do not extend into the sides of the hole or well, but act as a wedge if an attempt is made to lift the cover from the well opening.
Other patents which disclose specific devices for locking a cover in place over a hole exist. The Brewer U.S. Pat. No. 4,053,116 is directed to a cover which can be placed over an exposed tubular pipe in a road. A relatively large plate covers the excavation; and the cover includes a portion which extends downwardly into the exposed pipe to hold it in place. The plate, which is the primary cover over the opening, is very heavy, requiring construction equipment to lift it into place and to remove it when it no longer is needed.
The Clarke U.S. Pat. No. 3,426,659 is directed to a road excavation cover which is anchored in place by means of a horizontally arranged jack attached to the underside of the cover. The jack is operated to wedge the ends of the jack into engagement with the sides of the excavation to hold the cover in place; so that it cannot readily be moved or dislodged. This is not a hole cover for circular vertical holes.
It is desirable to provide a safety hole cover for holes which are drilled vertically into the ground for protecting the holes themselves from collapse, and further for preventing injuries to persons who otherwise might accidentally step into such a hole. It further is desirable to provide a such a hole cover which is portable, easy to install, relatively inexpensive, and which protects against unauthorized removal.